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Turning

Updated: Nov 5, 2023

Turning is a mechanical manufacturing process in which a raw workpiece is clamped in a rotating clamping device and then machined with a lathe. During the turning process, the workpiece is rotated around its own axis while the cutting tool is moved along the workpiece to remove material and create the desired shape.

Turning involves processing various types of workpieces, such as metal, plastics, wood and ceramics. The process is often used to create cylindrical or conical shapes, such as shafts, axles, bolts, nuts and other components.

It is important to make the correct selection and design of the angles and surfaces on the turning tool depending on the specific requirements of the machining process, the workpiece material and the cutting conditions.

Figure 1: Tool angle according to DIN 6581

The most important angles according to DIN 6581 are:

  • Principal cutting edge angle (ϰ): The Principal cutting edge angle is the angle between the tool cutting edge and a assumed working plane, e.g. B. the tool axis. It determines the inclination of the cutting edge in relation to the machining direction. A larger setting angle results in a more aggressive cut, while a smaller angle can produce a better surface finish.

  • Rake angle (γ): The rake angle is the angle between the rake surface and tool reference plane. It influences the type of chip formation. A positive rake angle (rake face behind the cutting edge) can lead to continuous chip formation, while a negative rake angle (rake face in front of the cutting edge) can lead to interrupted chip formation.

  • Flank angle (α): The flank angle is the angle between the rake surface and a reference plane perpendicular to the machining direction. It influences chip evacuation and cutting force. A larger clearance angle makes chip evacuation easier, while a smaller flank angle can lead to higher cutting force.

  • Wedge angle (β): The wedge angle is the angle between the rake surface and the flank surface. It influences the cutting force and the stability of the tool. A larger wedge angle can increase cutting force, while a smaller wedge angle can improve stability.

In addition to the angles, there are various faces on the rotary tool, including:

  • The rake surface in turning is the surface of the turning tool that comes into contact with the chip. It is located behind the cutting edge and plays an important role in chip formation and chip removal;

  • The relief surface in turning is the surface of the turning tool that is located between the cutting edge and the rake face. It allows the chip to pass through freely and influences chip evacuation and cutting force. The design of the open space is important to ensure efficient chip removal and good machining performance. There are different turning methods that are used depending on the requirements and the workpiece.


Turning processes


When it comes to turning, there are different processes and techniques that can be used depending on the requirements and the desired result (Figure 2).

Figure 2: Illustration of different turning processes

Here are some of the common turning methods:

1. Facing: During facing, the workpiece is machined lengthways to the axis of rotation. The cutting tool moves parallel to the axis of rotation and removes material to create the desired shape. Longitudinal turning is used for the production of cylindrical workpieces such as shafts, bolts and rods.

2. Chamfering: During chamfering, the cutting tool is moved transversely to the axis of rotation to machine the surface of the workpiece. This process is used to create flat, even surfaces, such as in the manufacture of faceplates or disks.

3. Thread cutting: During thread cutting, a thread is cut on the workpiece. For this purpose, a special thread cutting tool is used that penetrates the workpiece and forms the thread. Thread turning is used in various applications, from screws and nuts to threaded holes.

4. Parting off is a special turning process in which the workpiece is cut or tapped to separate it into separate parts. It is often used to cut workpieces to the desired length or to cut parts from a longer workpiece.

5. Contour turning is a turning process in which the workpiece is given a specific geometric shape or a complex profile. For this purpose, special tools are used that correspond to the desired profile of the workpiece.

6. Profile turning, in contrast to conventional turning, which gives the workpiece mainly cylindrical shapes, allows the production of more complex contours such as grooves, radii, conical surfaces and other contoured surfaces. During shape turning, the tool is guided along a given shape using CNC control to create the desired contour on the workpiece.

There are different types of lathes that are suitable for different requirements and workpieces. The most common types include the conventional lathe, the CNC (Computerized Numerical Control) lathe, and the automatic lathe.


Process parameters


Turning is a widespread process in industry, especially in metalworking. It enables the precise production of components with tight tolerances and can be used for both individual parts and series production. When turning and other machining processes, there are various important parameters that influence machining. The exact values of these parameters depend on various factors, such as the type of material, desired surface quality, tool geometry and other process conditions. Their arrangement in the working plane P can be seen in Figure 3.

Figure 3: Feeding or cutting movements when turning

Cutting speed (Vc) in meters per minute indicates how fast the workpiece moves relative to the cutting edge of the tool. The formula for the cutting speed when turning is:

The diameter of the workpiece (D) is usually measured in millimeters, and the speed (n) of the spindle is measured in revolutions per minute (rpm).

The feed rate (Vf) indicates how fast the tool moves along the workpiece. It is given in millimeters per revolution (mm/rev). The feed speed depends on many factors such as the cutting force, the type of material and the desired surface finish. The feed rate can be calculated using the following formula:

where f is feed per revolution.

The cutting depth (a) indicates how deeply the tool penetrates the workpiece. It is measured in millimeters. The cutting depth in turning can be calculated in various ways, depending on the specific requirements and parameters of the machining process. The cutting depth is determined by dividing the desired material removal per revolution by the number of cutting edges of the tool. A cutting depth that is too great can put undue stress on the tool and lead to premature wear or breakage. Therefore, it is important to determine the cutting depth according to the tool capacities and the requirements of the machining task.

The cutting width (b) is important because it directly influences the removal rate. A larger chip width leads to a higher removal rate, while a smaller chip width leads to a lower removal rate. The choice of the optimal chip width depends on various factors, including the material properties, the desired surface finish and the available machine power.

The chip thickness (h) during turning refers to the thickness of the material layer that is removed from the workpiece surface during the turning process. It is important to carefully monitor and control the chip surface during turning to achieve the desired machining quality and to protect the tool and workpiece from excessive stress.

The turning process is used for a variety of applications to produce rotationally symmetrical parts. The accuracy and surface quality of the workpiece depend on the careful adjustment of the cutting conditions and the selection of the correct tools. The turning process remains a fundamental and versatile manufacturing step in industrial production for the time being.

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